This invention relates to foamed innerspring units and, in particular, to a method of manufacturing foamed innerspring units wherein a flexible polyurethane foam is adhered directly to an innerspring.
As used herein, the term "foamed innerspring unit" is intended to be construed in its broadest sense. In general, such foamed innerspring units include mattresses and box springs. A mattress is designed to provide support for a person sleeping thereon, while a box spring provides support for both the mattress and the person sleeping on the mattress. However, other types of "foamed innerspring units" such as cushions, car seats and the like can be provided in accordance with the invention and the term "foamed innerspring unit" is not intended to be limited only to mattresses and box springs.
Innerspring units formed of a unitary construction are known. For example, in U.S. Pat. No. 3,239,584 issued to Terry et al. on Mar. 8, 1966, a method of fabricating a seat or cushion using a combination construction of springs and resilient pads is shown. A spring wire element with an open mesh fabric placed thereon is used and a resilient foam is foamed through the open mesh fabric to bond the spring wire element, the open mesh fabric and the foam into a unitary structure. The structure is used primarily to manufacture seats for vehicles.
In U.S. Pat. No. 3,920,609 issued to Lehmann on Nov. 18, 1975, a method of producing a spring core mattress using coil springs that are at least partially embedded in coverplates is shown. The coverplates are positioned so as to be substantially parallel to each other while the coil springs are under a preload and are surrounded by foam material to hold them in their respective relative positions. The foam material is provided as foam sheets and is not foamed directly onto the coverplates.
U.S. Pat. No. 3,325,834 issued to Lovett et al on June 20, 1967 shows a method of making an innerspring body supporting article. The innersprings are embedded in adhering particles of multicellular resilient spongy material in order to provide a sturdy long-lasting resilient unitary structure. The particles of resilient spongy material are coated with an adhesive prior to being deposited and pressed into a mold. The innerspring structure is completely covered with the coated particles and a unitary structure is formed when the adhesive sets. A divisional application of this patent issued as U.S. Pat. No. 3,452,127 on June 24, 1969.
Other spring reinforced mattresses wherein a foam or other type of resilient material completely surrounds an innerspring are shown, for example, in U.S. Pat. Nos. 2,994,890 issued to Wagner on Aug. 8, 1961; 3,099,021 issued to Wetzler on July 30, 1963; and 3,049,730 issued to Wall et al on Aug. 21, 1962. Wall et al specifically relates to a seat structure wherein a first layer of polyurethane foam is used to embed a spring. A second layer of a less dense polyurethane foam is provided on top of the first layer of foam in order to provide increased comfort.
The polyurethane foams discussed in Wall et al are formed by reacting a polymeric material and a suitable organic polyisocyanate. The polymeric material can be a polyester or polyesteramide such as may be obtained by condensing a variety of polybasic acids, preferably dibasic acids such as adipic, sebacic, phthalic, oxalic, malonic, succinic, maleic, fumaric, itaconic and the like with polyalcohols such as ethylene glycol, diethylene glycol, glycerol, sorbitol and/or amino alcohols such as ethanolamine and amino propanol. Alkylene glycols and polyoxyalkylene glycols which may be used include ethylene glycol, propylene glycol, styrene glycol, diethylene glycol, polypropylene glycol and copolymers of these glycols. A high grade castor oil may also be used.
Suitable organic polyisocyanates include toluene 2,4 diisocyanate, toluene 2,6 diisocyanate and mixtures thereof, naphthalene 1,5 diisocyanate and M-phenylene diisocyanate and mixtures of these materials. The use of a toluene diisocyanate identifies the process as "TDI chemistry".
U.S. Pat. No. RE 24,914 issued to Koenigsberg on Dec. 20, 1960 discloses an innerspring foam mattress. The mattress assembly includes an innerspring and slabs of flexible polyurethane foam foamed around the terminal portions of the innerspring. The foam is made from a polyalkylether prepolymer that is prepared by reacting polyalkylether with excess 2,4-toluene diisocyanate. A foam is then prepared from the prepolymer.
As noted above, the Koenigsberg foam is prepared using "TDI chemistry". Materials prepared by TDI chemistry are flammable and emit toxic fumes. Additionally, foams prepared using TDI chemistry have a tough, inflexible skin. Accordingly, such materials are not desirable for use in a mattress and to the best of applicants' knowledge, the Koenigsberg mattress has never been commercially available.
In recent years, "MDI chemistry" foam has become available. MDI chemistry uses the reaction between methylene diphenyl disso-cyanates (also known as diphenylmethane diisocyantes) and a polyol to form a urethane foam. When urethane foams for use in the manufacture of mattresses and the like are prepared using MDI chemistry, the problems associated with the use of TDI chemistry can be overcome.
U.S. Pat. No. 4,251,639 issued to Jarre et al on Feb. 17, 1981 relates to the manufacture of flexible foams using MDI chemistry. Urethane-modified aromatic polyisocyanates are used to prepare the foam. These polyisocyanates are obtained by a reaction of a mixture of diphenylmethane diisocyanates and polyphenylene polymethylene polyisocyanates and have an NCO content of 15 to 30% by weight and a viscosity of 100 to 2000 centipoises at 20.degree. C. The modified polyisocyanates are reacted with suitable hydroxyl compounds in a prepolymer or one-shot process in order to form flexible polyurethane foams having densities between about 20 and 150 grams per liter, the equivalent of between about 1.25 and 9.36 pounds per cubic foot.
The mixing of the components shown in Jarre et al can be accomplishing using conventional mixing equipment. For example, high pressure equipment which mixes the components of the foam at a pressure of between about 2,000 and 3,000 PSI can be used. Such equipment is extremely expensive and can cost upwards of $150,000 per machine.
Alternatively, low pressure mixing in a rotating mixer at a pressure of between about 50 and 100 PSI can be used. Such low pressure mixers comprise a cylinder with a mixing element that rotates at a speed of between about 4,000 and 8,000 rpm. This equipment is a bit less expensive than high pressure equipment and generally costs between about $50,000 and $100,000 per machine.
It is, therefore, desirable to provide a foamed innerspring unit that can be manufactured in a practical and continuous molding operation.